1. Field of the Invention
This invention relates to a replaceable lamp assembly for an automotive headlamp. More particularly, this invention relates to a replaceable lamp assembly which comprises an incandescent lamp having a flat press seal at one end mounted on a thermoplastic base by means of a holder made of a single piece of sheet metal clamped around the flattened end of the lamp and secured to the plastic base by RF welding.
2. Background of the Invention
Replaceable lamp assemblies for automotive headlamps comprising an incandescent lamp, such as an incandescent-halogen lamp, mounted on a thermoplastic base or holder body of substantially tubular shape which is mounted to a reflector in an automotive vehicle are well known to those skilled in the art. The base or holder body is precision molded from a thermoplastic material in order to achieve dimensional accuracy and low cost. The filament of the lamp must be accurately positioned with respect to the thermoplastic base so that a predetermined light distribution will result when the lamp assembly is installed in the reflector portion of an automotive vehicle. Invariably this means that if only one filament is employed, then that filament must reside at the focal center of the reflector. Where two filaments are employed in the lamp for a high beam and a low beam, one filament will generally be at the focal center of the reflector and the other filament will be offset by a certain amount in order to assure the proper light pattern emanating forward of the reflector. These replaceable lamp assemblies generally have a flange on the base portion which butts against a rearwardly protruding nose portion of the automotive lamp reflector to insure precise alignment of the assembly with respect to the reflector. Thus, the filament of the lamp must be accurately positioned with respect to the flange which fits or butts against the rear nose portion of the reflector so that a predetermined light distribution will result when the lamp assembly is installed in an automotive vehicle. Some lamps used in such assemblies are connected to a base without the use of a cement or adhesive.
Typically, such lamps comprise vitreous, light transmissive envelopes made of a high temperature glass or a high purity fused silica (quartz) which terminates at the bottom end in a pinch or press seal. An exhaust tip through which the interior of the lamp envelope is exhausted and a fill gas introduced may be present at either the top or bottom end of the lamp envelope as is well known to those skilled in the art. Electric current supply leads extend outwardly of the press seal and at least one incandescent filament is located interiorly of the lamp envelope electrically connected to the current supply leads. One end of a sheet metal lamp holder clamps around the flat pinch or press seal of the lamp and is coupled at its other end to the plastic base. The plastic base is generally cylindrical in shape having two internal cavities, each open at one end with a wall separating the two cavities through which connecting terminals for the lamp extend which are electrically connected to the lamp current supply leads at one end and to a male electric plug at the other end. Such replaceable automotive lamp assemblies presently available employ at least two or three metal parts to form a lamp holder unit for connecting or coupling the incandescent lamp to the plastic base. Such multiple part construction requires multiple assembly steps and parts. Typical prior lamp assemblies are disclosed, for example, in U.S. Pat. Nos. 4,719,543; 4,950,942; 4,864,183; 4,769,574, 4,751,421 and 4,528,619.
Construction of a typical replaceable automotive lamp assembly presently available and used is illustrated in perspective view in FIG. 1. Thus, lamp 100 is secured into thermoplastic base 102 by means of lamp holder 104. Flange 106 serves to accurately position the lamp assembly into an automotive reflector by acting as a stop when inserting the assembly into the rear of the reflector. O-ring 108 is made of a heat resistant elastomeric material, such as a silicone rubber, and serves to provide a hermetic seal of the lamp assembly into the reflector. A resinous, heat resistant potting compound (such as a silicone) is applied inside the bottom cavity adjacent the wall separating both cavities of the base to hermetically seal the electrical terminals molded into the wall. Plug 110, which is not a part of the lamp assembly, plugs into the bottom cavity where it contacts terminals for wires 112 to make electrical connection to the lamp. Turning to FIG. 2, lamp holder 104 is shown in more detail in perspective view and lamp 100 is shown in partial phantom view merely to illustrate lamp filaments 114 and 116. Thus, lamp holder 104 comprises a metal clamp 118 which is clamped around the flattened pinch seal base or bottom portion (not generally shown) of lamp 100 as an assembly of two rectangular sheet metal straps 123 and 124 which are clamped around the flattened lamp end portion, bent and welded together at 120 and 122. Clamp 118, in turn, is secured to metal cup 130 by means of welding, of which only welds 126 and 128 are shown for metal strap 124. Metal cup 130, in turn, is secured to metal sleeve 105 by means of welding (i.e., 136 and 137) to four strap portions of which only two, 132 and 134 are shown. Wire connectors 140, 142 and 144 extend downwardly from lamp 100 to make electrical connection with respective terminals in base 102. To couple lamp 100 to plastic base 102, lamp 100 is mechanically secured by means of welding clamp 118 around the pinch seal of the lamp which, in turn, is welded to metal cup 130. Metal sleeve 104, being made of sheet steel, is secured to the interior walls of the upper cavity in plastic base 102 by adhesive or RF welding. The preassembled lamp 100, clamp 118 and cup 130 are then positioned within and adjacent the strap portions of sleeve 104 as shown and wires 140, 142 and 144 are soldered to respective terminals in base 102. The position of the lamp, clamp and cup subassembly is then adjusted while at least one filament is energized in order to accurately position the filament radially with respect to the longitudinal central axis of the replaceable lamp assembly and also with respect to its distance from flange 106. Once the filament has been accurately positioned, cup 130 is welded to the strap portions of sleeve 104 in order to secure the lamp to the base.
Accordingly, it would be a significant advance to the art if one could reduce the number of parts, manufacturing steps and concomitant costs in the manufacture and assembly of such replaceable automotive lamp assemblies.